U.S. patent number 5,610,715 [Application Number 08/412,309] was granted by the patent office on 1997-03-11 for displacement detecting system, an expose apparatus, and a device manufacturing method employing a scale whose displacement is detected by a selected detection head.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Kyoichi Miyazaki, Seiji Takeuchi, Minoru Yoshii.
United States Patent |
5,610,715 |
Yoshii , et al. |
March 11, 1997 |
**Please see images for:
( Certificate of Correction ) ** |
Displacement detecting system, an expose apparatus, and a device
manufacturing method employing a scale whose displacement is
detected by a selected detection head
Abstract
A displacement detecting system includes a scale provided on a
surface of a movable object and having a diffraction grating formed
along a predetermined direction, a head unit disposed above the
surface of the movable object and having a plurality of detection
heads, for detecting displacement of the scale in the predetermined
direction, the detection heads being disposed along a direction
different from the predetermined direction, and a selecting device
for selecting at least one detection head out of the detection
heads, for detection of a displacement of the scale in the
predetermined direction.
Inventors: |
Yoshii; Minoru (Tokyo,
JP), Miyazaki; Kyoichi (Utsunomiya, JP),
Takeuchi; Seiji (Utsunomiya, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
13148783 |
Appl.
No.: |
08/412,309 |
Filed: |
March 29, 1995 |
Foreign Application Priority Data
|
|
|
|
|
Mar 30, 1994 [JP] |
|
|
6-060662 |
|
Current U.S.
Class: |
356/499 |
Current CPC
Class: |
G03F
7/70775 (20130101); G03F 9/70 (20130101) |
Current International
Class: |
G03F
9/00 (20060101); G03F 7/20 (20060101); G01B
009/02 () |
Field of
Search: |
;356/356,358,363 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Turner; Samuel A.
Assistant Examiner: Merlino; Amanda
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. A displacement detecting system, comprising:
a scale provided on a surface of a movable object and having a
diffraction grating formed along a predetermined direction;
a head unit disposed above the surface of the movable object and
having a plurality of detection heads, for detecting displacement
of said scale in said predetermined direction, said detection heads
being disposed along a direction different from said predetermined
direction; and
selecting means for selecting at least one detection head out of
said detection heads, for detection of a displacement of said scale
in said predetermined direction.
2. A system according to claim 1, wherein the width of said
diffraction grating in the direction along which said detection
heads are disposed, is sufficiently wide so that at least two
detection heads of said detection heads of said head unit directly
face said diffraction grating.
3. A system according to claim 1, wherein each of said detection
heads comprises a light source for providing coherent light,
projecting means for projecting the coherent light from said light
source onto said diffraction grating, and detecting means for
detecting interference light produced as a result of interference
of diffraction light of predetermined orders having been diffracted
by said diffraction grating.
4. An exposure apparatus for printing circuit patterns on a wafer
sequentially while moving the wafer, said apparatus comprising:
a movable stage on which the wafer is to be placed;
a scale provided in a portion of a surface of said movable stage,
other than a portion on which the wafer is to be placed, said scale
having a diffraction grating formed along a predetermined
direction;
a head unit disposed above said movable stage and having a
plurality of detection heads, for detecting displacement of said
scale in said predetermined direction, said detection heads being
disposed along a direction different from said predetermined
direction; and
selecting means for selecting at least one detection head out of
said detection heads, for detection of a displacement of said scale
in said predetermined direction.
5. An apparatus according to claim 4, wherein the width of said
diffraction grating in the direction along which said detection
heads are disposed, is sufficiently wide so that at least two
detection heads of said detection heads of said heat unit directly
face said diffraction grating.
6. An apparatus according to claim 4, wherein each of said
detection heads comprises a light source for providing coherent
light, projecting means for projecting the coherent light from said
light source onto said diffraction grating, and detecting means for
detecting interference light produced as a result of interference
of diffraction light of predetermined orders having been diffracted
by said diffraction grating.
7. A device manufacturing method wherein circuit patterns are
printed on a wafer, coated with a photosensitive material,
sequentially while moving the wafer, said method comprising the
steps of:
placing the wafer on a movable stage; and
detecting displacement of a scale in a predetermined direction;
wherein the scale is formed on the movable stage at a position
different from the wafer on the movable stage, and has a
diffraction grating formed along the predetermined direction;
and
wherein said detecting step includes selecting at least one of
detection heads of a head unit, disposed above the movable stage,
for detecting displacement of the scale in the predetermined
direction, the detection heads being disposed along a direction
different from the predetermined direction.
Description
FIELD OF THE INVENTION AND RELATED ART
This invention relates to a displacement detecting system for
detecting the amount of displacement of a movable member along a
two-dimensional plane. According to another aspect; the invention
is concerned with an exposure apparatus having such displacement
detecting system, and with a device manufacturing method which uses
such exposure apparatus.
The manufacture of semiconductor devices such as ICs or liquid
crystal displays includes a process of transferring a circuit
pattern formed on an original, such as a reticle or photomask, onto
a resist coated wafer by means of a semiconductor exposure
apparatus.
As such exposure apparatus, step-and-repeat type exposure
apparatuses or step-and-scan type exposure apparatuses having a
printing chip size as .sqroot.2 times larger, are well known.
FIG. 1 is a schematic side view of a known type step-and-repeat
semiconductor exposure apparatus. As illustrated in FIG. 1, the
apparatus comprises a moving mechanism having an X stage 1007 and a
Y stage 1006. The moving mechanism is provided with a mirror
support 1021 for supporting a measurement light path mirror 1023,
to be described below. The mirror supporting member 1021 supports a
bearing means 1010 through a tilt mechanism 1008. Mounted on the
bearing means 1010 is a wafer chuck 1005 for holding a wafer 1004
on its top surface. The wafer chuck 1005 is supported movably along
a Z axis, through a fine Z motion mechanism 1009. Thus, the wafer
chuck 1005 is movable along the X and Y directions, and also its
position with respect to the Z direction as well as its tilt with
respect to the X-Y plane can be adjusted minutely.
Disposed above the wafer chuck 1005 are an original 1003 having a
circuit pattern formed thereon placed opposed to the wafer 1004, a
light source 1001 for projecting the circuit pattern of the
original 1003 onto the wafer 1004, and a barrel 1002 having a
reduction projection optical system, for projecting an optical
image, formed by the passage of light from the light source 1001
through the original 1003, onto the wafer 1004 in a reduced
scale.
Laser distance measuring device 1020 is a component of a
displacement detecting system for detecting the relative positional
relationship between the mirror support 1021 and the barrel 1002
along the X-Y plane. The laser distance measuring device 1020
includes a measurement light path mirror 1023 supported by the
mirror support 1021, a laser light source 1022 for projecting laser
light to the measurement light path mirror 1023, a reference light
path mirror 1024 mounted on the barrel 1022, a half mirror 1025 for
dividing the laser light from the laser light source 1022 into
measurement light and reference light, and a light path vending
mirror for deflecting the reference light divided by the half
mirror 1025 toward the reference light path mirror 1024.
The laser light projected by the laser light source 1022 is divided
by the half mirror 1025 into the reference light and the
measurement light, which are then reflected by the reference light
path mirror 1024 and the measurement light path mirror 1023,
respectively, back to the laser light source 1022. By comparing the
phases of these lights, the position of the mirror support 1021
relative to the barrel 1022 is detected.
For performing the exposure process, first a wafer 1004 coated with
a resist is fixed to the wafer chuck 1005, and, by means of the
tilt mechanism 1008 and/or the fine Z motion mechanism 1009, the
inclination of the wafer surface and/or the position thereof with
respect to the Z direction is adjusted. Then, the light source 1001
is turned on such that the circuit pattern as a whole of the
original 1003 is projected at once in a reduced scale onto the
wafer 1004, whereby the circuit pattern is printed on the wafer.
Subsequently, the X stage 1007 and the Y stage 1006 are moved
stepwise by a predetermined distance to move and change the
exposure region, while measuring the position of the mirror support
1021 through the laser distance measuring device 1022. Then, the
light source 1001 is turned on again, and the exposure operation is
performed again. This process is repeated, and finally, circuit
patterns are printed on the whole surface of the wafer 1004.
As compared therewith, the step-and-scan process is a process in
which one circuit pattern is divided into plural blocks which are
scanned sequentially in a timed relation with a wafer for exposure
of it, rather than exposing the whole circuit pattern at once. To
this end, a plate member having a slit formed therein is disposed
between a light source and an original, and the original is made
movable along a direction perpendicular to the lengthwise direction
of the slit. Only a slit-like portion of the circuit pattern as
illuminated is projected on a wafer and, simultaneously therewith,
the original and the wafer are scanningly moved in a timed relation
in a direction perpendicular to the lengthwise direction of the
slit, such that the circuit pattern as a whole, formed on the
original, is printed on the wafer. After this, the stage is moved
stepwise by a predetermined distance to move and change the
exposure region, and the above-described exposure operation is
repeated. This is essentially the same as with the step-and-repeat
exposure process.
A large scaled integrated circuit (LSI) as represented by a DRAM,
for example, is manufactured generally with processes of a number
not less than twenty (20). In these processes, a technique is
necessary for overlaying a circuit pattern of a current process
upon a circuit pattern formed through a preceding process. An
automatic alignment process is a process to this end, for
automatically aligning an optical image of an original formed by a
reduction optical system with a circuit pattern formed on a
wafer.
In the first process, as a circuit pattern is printed on a resist
of a wafer, alignment marks to be used for the alignment operation
are printed on the wafer together with the circuit pattern, in an
outside (finally unnecessary) area of the circuit pattern, which
area is called a scribe line. Then, through chemical and heat
treatments, a predetermined structure is produced thereat. This is
the process to be performed initially. Subsequently, a resist is
applied again to this wafer, and the wafer is placed on a wafer
stage. Then, while moving the stage, the position of an alignment
mark is detected by means of an alignment mark detecting system
having a TV camera, for example, and the stage is positioned. The
position of the mark is then measured by means of a laser distance
measuring device for measuring the position of the wafer stage.
This operation is performed with respect to each alignment mark.
The results are then statistically processed, and distortion of the
wafer is calculated and the position to which the wafer stage is to
be moved is determined. Then, while relying on the amount of
movement of the laser distance measuring device, the wafer stage is
moved to the thus determined position, for the position for
exposure of a next circuit pattern, and then the exposure operation
is performed. As described, it is very important for exposure of a
wafer to detect the wafer position accurately.
On the other hand, as a displacement detecting system for detecting
the amount of movement of a movable member very precisely, there is
a displacement detecting system based on the principle of
diffraction grating interference. An example is disclosed in
Japanese Laid-Open Patent Application, Laid-Open No. 215515/1993,
which will be explained below with reference to FIG. 2.
In FIG. 2, a semiconductor laser 211 is disposed at a predetermined
distance from a movable member 222 having a diffraction grating 216
is provided on its surface. There are two mirrors 214a and 214b for
deflecting coherent light, produced from an active layer of the
semiconductor laser 211, toward one point in a space (on the
diffraction grating 216), as well as detecting means 215 for
receiving diffraction light from the diffraction grating 216. The
surface of the active layer 212 is placed substantially in parallel
to the surface of the diffraction grating 216, and the light
receiving surface of the detecting means 215 is placed
substantially in parallel to the surface of the active layer 212.
These optical components are disposed so that two laser lights 231a
and 231b from the mirrors 214a and 214b intersect with each other
within a plane perpendicular to the surface of the active layer
212.
When in the structure described above the active layer 212 of the
semiconductor laser 211 is excited, photons are produced and some
of them repeatedly go back and forth within the active layer 212.
During this process, light amplification occurs and a portion goes
through a resonator 213a and emits light as laser light. The laser
light is emitted from the opposite sides of the active layer 212,
and emitted rays are reflected by the mirrors 214a and 214b toward
a single point in space where the diffraction grating 216 is
disposed. Since the surface of the active layer 212 is placed
parallel to the diffraction grating 216, the occupied space in the
direction perpendicular to the plane on which the light is incident
is small. Here, the light expands largely in a plane perpendicular
to the thickness of the active layer, that is, in a plane parallel
to the sheet of the drawing. As a result, the light is not incident
on the outside of the diffraction grating 216 but is efficiently
incident on the diffraction grating 216 and is diffracted thereby.
Consequently, the diffraction light (signal light) increases, which
in turn leads to an increase in light impinging on the light
receiving means. Thus, the light reception efficiency increases and
the signal-to-noise ratio (S/N ratio) increases, such that the
detection precision is enhanced.
As the light reflected by the mirror 214a or 214b is projected on
the diffraction grating 216, the reflected light impinges on the
diffraction grating so that m-th order diffraction light (m is an
integer) from the diffraction grating 216, to be detected, is
reflected therefrom substantially perpendicularly to the
diffraction grating 216. Namely, if the pitch of the diffraction
grating 216 is P, the wavelength of the coherent light is .lambda.,
and the incidence angle of the coherent light upon the diffraction
grating 216 is .theta..sub.m, then the light is projected on the
diffraction grating to satisfy the following relation:
Also, two diffraction light beam of positive and negative m-th
orders, being substantially perpendicularly projected from the
diffraction grating 216, are superposed one upon another and are
projected on the light receiving means 215. The detecting means 215
detects the thus interfering lights. More specifically, the
detecting means 215 detects the number of brightness/darkness
patterns (pulses) of the interference fringe which corresponds to
the movement state of the diffraction grating 216. Here, the light
receiving surface of the detecting means 215 is placed
perpendicularly to the light impinging thereon, to enhance the
light reception efficiency.
Higher and higher precision has been required for the alignment
between an optical image of an original and a wafer, in
consideration of further increases in the density and integration
of each semiconductor device. The currently required alignment
precision is 0.05 micron, for example. On the other hand, since a
laser distance measuring device is based on the wavelength of a
laser propagated within an air, there is a problem of instability
of a measured value of about 0.03 micron due to any environmental
disturbance, such as the fluctuation of air or the non-uniformness
of temperature or pressure, for example.
There might be an exposure apparatus having a displacement
detecting system such as shown in FIG. 2 for measuring the amount
of movement of a stage without using a laser distance measuring
device. More specifically, as shown in FIG. 3, a two-dimensional
grating scale 1122 comprising an X-axis and Y-axis two-dimensional
diffraction grating may be provided on the surface of a wafer chuck
1105 and, also, four heads 1121 each having a semiconductor laser
similar to that used in the example of FIG. 2 are mounted on the
lower end portion of a barrel 1102, a pair being set in the X
direction and another pair being set in the Y direction, so as to
detect the amount of displacement of the wafer chuck 1105 along the
X-Y plane. In this structure, the distance along which the laser
goes through the air becomes shorter. Therefore, with this
structure, the effect of any disturbance of the air may be reduced
and stable measurement may be assured.
However, if such a displacement detecting system is used in an
exposure apparatus, for detecting displacement of a wafer, it will
be necessary that in consideration of the movement amount of a
wafer or the movement precision thereof, a two-dimensional grating
scale has a size of about 150 mm.times.150 mm (X- and Y-direction
lengths) and a diffraction grating pitch of 2 microns both in the X
direction and the Y direction. It is practically very difficult to
prepare such a large size two-dimensional grating scale. Also, a
large size two-dimensional grating will be fragile, and will be
difficult to handle.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a
displacement detecting system capable of detecting the amount of
movement along two-dimensional directions correctly, without use of
a laser distance measuring device or a two-dimensional diffraction
grating.
It is another object of the present invention to provide an
exposure apparatus in which, by use of such a displacement
detecting system, a wafer can be positioned very precisely.
It is a further object of the present invention to provide a device
manufacturing method which uses such an exposure apparatus.
In accordance with an aspect of the present invention, to achieve
at least one of these objects, there is provided a displacement
detecting system, comprising: a scale provided on a surface of a
movable object and having a diffraction grating formed along a
predetermined direction; a head unit disposed above the surface of
the movable object and having a plurality of detection heads, for
detecting displacement of the scale in the predetermined direction,
the detection heads being disposed along a direction different from
said predetermined direction; and selecting means for selecting at
least one detection head out of the detection heads, for detection
of a displacement of the scale in the predetermined direction.
In one preferred form of this aspect of the present invention, the
width of the diffraction grating in the direction along which the
detection heads are disposed, may correspond to the width opposed
by at least two detection heads of the detection heads of the head
unit.
In this or another preferred form of this aspect of the present
invention, each of the detection heads may comprise a light source
for providing a coherent light, projecting means for projecting the
coherent light from the light source onto the diffraction grating,
and detecting means for detecting interference light produced as a
result of the interference of diffraction light of predetermined
orders having been diffracted by said diffraction grating.
In accordance with another aspect of the present invention, there
is provided an exposure apparatus for printing circuit patterns on
a wafer sequentially while moving the wafer, the apparatus
comprising: a movable stage on which the wafer is to be placed; a
scale provided in a portion of a surface of the movable stage,
other than a portion on which the wafer is to be placed, the scale
having a diffraction grating formed along a predetermined
direction; a head unit disposed above the movable stage and having
a plurality of detection heads, for detecting displacement of the
scale in the predetermined direction, the detection heads being
disposed along a direction different from the predetermined
direction; and selecting means for selecting at least one detection
head out of the detection heads, for detection of a displacement of
the scale in the predetermined direction.
In one preferred form of this aspect of the present invention, the
width of the diffraction grating in the direction along which the
detection heads are disposed, may correspond to the width opposed
by at least two detection heads of the detection heads of the head
unit.
In this or another preferred form of this aspect of the present
invention, each of the detection heads may comprise a light source
for providing a coherent light, projecting means for projecting the
coherent light from the light source onto the diffraction grating,
and detecting means for detecting interference light produced as a
result of the interference of diffraction light of predetermined
orders having been diffracted by the diffraction grating.
In accordance with a further aspect of the present invention, there
is provided a device manufacturing method wherein circuit patterns
are printed on a wafer, coated with a photosensitive material,
sequentially while moving the wafer, the method comprising the
steps of: placing the wafer on a movable stage; and detecting
displacement of a scale in a predetermined direction; wherein the
scale is formed on the movable stage at a position different from
the wafer on the movable stage, and has a diffraction grating
formed along the predetermined direction; and wherein the detecting
step includes selecting at least one of detection heads of a head
unit, disposed above the movable stage, for detecting displacement
of the scale in the predetermined direction, the detection heads
being disposed along a direction different from the predetermined
direction.
These and other objects, features and advantages of the present
invention will become more apparent upon a consideration of the
following description of the preferred embodiments of the present
invention taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side view of a known type exposure
apparatus,
FIG. 2 is a schematic side view of a known type displacement
detecting system,
FIG. 3 is a schematic view for explaining a case where the
displacement detecting system shown in FIG. 2 is incorporated into
the exposure apparatus shown in FIG. 1,
FIG. 4 is a schematic side view of a displacement detecting system
according to a first embodiment of the present invention, which is
incorporated into an exposure apparatus.
FIG. 5 is a perspective view, schematically showing a main portion
of the exposure apparatus of FIG. 4.
FIG. 6 is a perspective view, schematically showing a displacement
sensor of the exposure apparatus of FIG. 4, as viewed from the
below.
FIGS. 7A and 7B are schematic side views of the displacement sensor
of FIG. 6, respectively, wherein FIG. 7A shows it as viewed in the
Y direction while FIG. 7B shows it as viewed in the X
direction.
FIGS. 8A and 8B are schematic views, respectively, for explaining
the positional relation among wafer head units of the exposure
apparatus shown in FIG. 4 and the positional relation among wafer
scales of the exposure apparatus.
FIG. 9 is a perspective view of a wafer head unit of the exposure
apparatus shown in FIG. 4, as viewed from the below.
FIG. 10 is a schematic view of a control means for wafer head units
of the exposure apparatus shown in FIG. 4.
FIG. 11 is a perspective view, for explaining the positional
relation among wafer head units and wafer scales during an exposure
operation in the exposure apparatus of FIG. 4.
FIG. 12 is a schematic view of a displacement detecting system
according to a second embodiment of the present invention, which is
incorporated into an exposure apparatus.
FIGS. 13A and 13B are schematic views, respectively, for explaining
the positional relation among the wafer scales of the exposure
apparatus of FIG. 12 and the positional relation among the wafer
head units of the exposure apparatus, respectively, wherein in FIG.
13A is a view of barrel from the below and in FIG. 13B is a view of
a wafer chuck from the above.
FIG. 14 is a flow chart of device manufacturing processes.
FIG. 15 is a flow chart for explaining details of a wafer process
of the processes shown in FIG. 15.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described
with reference to the drawings.
[First Embodiment]
FIG. 4 is a schematic side view of a displacement detecting system
according to a first embodiment of the present invention, which is
incorporated into an exposure apparatus. FIG. 5 is a perspective
view, schematically showing a main portion of the exposure
apparatus of FIG. 4.
The exposure apparatus of this embodiment is of step-and-scan type,
and it comprises a movement mechanism having an X stage 7 movable
in the X direction and a Y stage 6 movable in the Y direction.
Also, it has a bearing means 10 which is supported by a tilt
mechanism 8 for tilt adjustment with respect to the X-Y plane.
Wafer chuck 5 for holding a wafer 4 thereon is supported by this
bearing means 10 through a fine Z motion mechanism 9 which is
expandable and contractible in the Z direction. Thus, the wafer
chuck 5 provides a movable member whose position with respect to
the X, Y and Z directions as well as its tilting with respect to
the X-Y plane are adjustable.
Disposed above the wafer 4 held by the wafer chuck 4 is an original
3 having a circuit pattern formed thereon, which pattern is to be
transferred to the wafer 4. The original 3 is held by an original
holder 11 which is movable in the Y direction. Disposed above the
original 3 is a light source 1. Disposed between the original 3 and
the wafer chuck 5 is a barrel (stationary member) 2 including a
reduction optical system for projecting an optical image of the
circuit pattern of the original 3, as formed by the passage of
light from the light source 1 through the original 3, onto the
wafer 4 at a reduced scale.
Original scales 24 each having a one-dimensional diffraction
grating are fixedly mounted onto the opposite end faces of the
original holder 11 which faces are parallel to the Y direction.
Also, fixedly mounted at the positions on the top end face of the
barrel 2 opposed to the original scales 24, are original heads 23
each for detecting the amount of movement of the original holder 11
relative to the barrel 2 on the basis of the interference of light
at the diffraction grating of corresponding one of a the original
scales 24. The structure of the original scales 24 and the original
heads 23 as well as the principle of displacement detection by them
are similar to those of the displacement detecting system of FIG.
2. Therefore, an explanation of them will be omitted here.
Disposed between the light source 1 and the original 3 is a plate
member 18 having a slit 18a extending along the X direction.
Mounted on the bottom face of the barrel 2 are four displacement
sensors 25. These displacement sensors 25 are operable to measure
the distance between the wafer 4 as held by the wafer chuck 5 and
the lower end of the barrel 2 in accordance with the principle of
triangular measurement to thereby determine the position of the
wafer 4 in the Z direction. Here, the details of the displacement
sensor 25 will be explained with reference to FIGS. 6 and 7.
As best seen in FIG. 6, on a base 251 made of silicone, for
example, there are a detecting means 252 comprising a CCD line
sensor, a light source means 255 comprising a semiconductor laser,
an optical member 254 which serves to collect a divergent light
beam 255a (see FIG. 7) emitted from the light source means 255,
with respect to the Z direction and which also serves to diverge in
the same manner in the Y direction so that it provides a linear
light beam elongated in the Y direction, and a mirror 253 for
reflecting the light from the optical member 254 and for projecting
the same obliquely upon the wafer 4 to be measured (see FIG. 7),
with a predetermined angle, as a light spot. These components are
formed on the base 251 integrally therewith.
In the structure described above, as shown in FIG. 7, the divergent
light 255a emitted by the light source means 255 is transformed by
the optical member 254 into a linear light beam elongating in the Y
direction. This light is reflected by the mirror 253, and the
reflected light impinges on the wafer 4. The light is then
reflected by the wafer 4, and the reflected light impinges on the
detecting means 252. The detecting means 252 serves to detect the
light quantity gravity center position of the incident light 255c,
and to determine the position coordinates of the incidence position
of the light upon the detecting means 252. The optical arrangement
is so set that, when the spacing between the wafer 4 and the
position sensor 25 is at a predetermined level, the light impinges
on a predetermined position upon the detecting means 252. Thus, by
detecting the position coordinates of the incidence position of the
light upon the detecting means 252, the spacing to the wafer 4 is
detected.
Referring back to FIGS. 4 and 5, four wafer head units 21a, 21b,
21c and 21d are mounted on the outer circumferential surface at the
lower end of the barrel 2. Fixedly mounted on the top face of the
wafer chuck 5, around the wafer 4, are corresponding four wafer
scales 22a, 22b, 22c and 22d. More specifically, as best seen in
FIG. 8A, of the wafer head units 21a, 21b, 21c and 21d, two wafer
head units 21a and 21b have their elongating directions parallel to
the X direction, and they are disposed diametrically opposed to
each other with respect to the central axis of the barrel 2. The
remaining two wafer head units 21c and 21d have their elongating
directions parallel to the Y direction, and they are disposed
diametrically opposed to each other with respect to the central
axis of the barrel 2.
Also, as best seen in FIG. 8B, each of the wafer scales 22a, 22b,
22c and 22d has a size of about 150 mm.times.150 mm (in length and
width), and each wafer scale has a one-dimensional diffraction
grating which is defined by forming, on a quartz substrate, short
straight nickel chrome patterns of 1-micron widths, arrayed in the
scale lengthwise direction at a pitch of 2 microns. Of these wafer
scales 22a, 22b, 22c and 22d, two wafer scales 22a and 22b
correspond to the wafer head units 21a and 21b having their
elongating directions parallel to the X direction, and these wafer
scales 22a and 22b are fixed so that their elongating directions
are parallel to the Y direction. The other two one-dimensional
wafer scales 22c and 22d correspond to the wafer head units 21c and
21d having elongating directions parallel to the Y direction, and
these wafer scales 22c and 22d are fixed so that their elongating
directions are parallel to the X direction. Also, each wafer scale
has its surface placed at substantially the same level as the
surface of the wafer or the surface of the wafer chuck with respect
to the Z direction.
Details of the wafer head units 21a, 21b, 21c and 21d will be
explained, while taking one wafer head unit (21a) as an
example.
FIG. 9 is a perspective view of the wafer head unit 21a, as viewed
from below. FIG. 9 also depicts the relation of the wafer head unit
21a with the corresponding wafer scale 22a. The wafer head unit 21a
comprises, as shown in FIG. 8A or 8B, a number of element heads 210
being juxtaposed and adjoined in the lengthwise direction of the
wafer head unit. At least two of the element heads 210 face to the
wafer scale 21a, constantly. In other words, the wafer scale 22a
has such a width that it is opposed to at least two element heads
210. Each of the element heads 210 has a similar structure as the
semiconductor laser having been described with reference to FIG. 2.
Also, the principle of displacement detection by using these
element heads 210 is similar to that having been described with
reference to FIG. 2. Therefore, a description of them will be
omitted here.
Two wafer head units 21a and 21b having lengthwise directions
parallel to the X direction, serve to detect the amount of movement
of the wafer chuck 5 in the Y direction. The other two head units
21c and 21d having lengthwise directions parallel to the Y
direction, serve to detect the amount of movement of the wafer
chuck 5 in the X direction. It is to be noted that, while in this
embodiment these two pairs of wafer head units (and thus the two
pairs of wafer scales) are elongated along orthogonal directions (X
and Y directions), this is not always necessary. What is necessary
is that the two pairs of the wafer head units (or wafer scales)
extend along different directions.
FIG. 10 illustrates the structure of control means 30 for
controlling the wafer head unit 21a. As described hereinbefore, the
wafer head unit 21a comprises a plurality of element heads 210, and
the outputs of these element heads 210 are applied through an array
relay switch 31 to a head controller 32. The head controller 32
serves to discriminate one or those of the element heads 210 which
is or are operable to perform the detection, on the basis of the
light quantity of the reflected light, of the light directed to the
one-dimensional diffraction grating of the wafer scale 22a (see
FIG. 8A or 8B). Here, the head controller 210 signals a relay
switch controller 33 so as to fetch outputs of at least two element
heads 210 simultaneously. In response to the signal from the head
controller 32, the relay switch controller 33 operates to connect
the relays for at least two of the element heads 210 which are to
be made active, and supplies to the head controller 32 a dual phase
interference signal, which includes the direction.
It will be understood from the foregoing description that the
displacement detecting system of this embodiment of the present
invention is provided by the wafer head units 21a, 21b, 21c and
21d, the wafer scales 22a, 22b, 22c and 22d, and the control means
30.
Next, the operation of the exposure apparatus of according to this
embodiment will be explained.
First, a wafer 4 coated with a resist is placed and fixed onto the
wafer chuck 5, and by using the displacement sensors 25 the
position of the wafer 4 in the Z direction is detected. Here, the
position or tilt of the wafer 4 deviates from a predetermined
position, and the tilt mechanism 8 and/or the fine Z motion
mechanism 9 is used to adjust the position of the wafer chuck 5,
toward the predetermined position.
Subsequently, a circuit pattern of an original 3 is projected onto
the wafer 4 at a reduced scale, so as to print the circuit pattern
on the wafer. Here, the light from the light source 3 is projected
onto the original 3 through the slit 18a and, therefore, a portion
of the circuit pattern of the original 3 is projected, in a
slit-like form, onto the wafer. Simultaneously with this exposure
of the wafer 4, the original 3 and the wafer 4 are moved in a timed
relation with a speed difference corresponding to the reduction
magnification of the reduction optical system of the barrel 2, by
which the whole of one original 3 is printed on the wafer 4, in a
region corresponding to one chip. Thereafter, the X stage 7 and the
Y stage 8 are moved stepwise through a predetermined distance to
shift the exposure region on the wafer 4, and the above-described
exposure operation is repeated. This is essentially the same as
that of the step-and-repeat exposure process.
The movement of the original 3 is performed by moving the original
holder 11 while detecting diffraction light from the diffraction
grating of the original scale 24 by use of the original head 23. As
regards the scan of the wafer 4, although details will be explained
later, the principle thereof is basically the same as the scan of
the original 3.
FIG. 11 is a perspective view for explaining the positional
relationship between the wafer head units and the wafer scales
during the exposure operation of the exposure apparatus shown in
FIG. 4.
In FIG. 11, as the wafer chuck 5 moves in the negative Y direction,
the wafer scales 22a, 22b, 22c and 22d also move in the negative Y
direction. Here, of the wafer head units 21a, 21b, 21c and 22d,
those (head units 21a and 21d) which are overlying associated wafer
scales operate to read the amount of movement of these wafer scales
22a and 21d. Here, the element heads of one wafer head unit 21a
operate to detect the amount of movement of the wafer scale 22a
along the Y direction. As regards the other wafer head unit 21d,
since the wafer scale 22d moves along the Y direction, it operates
so that, when one element head and an adjacent element head
provides detected values at the same time, the detected values with
respect to the X direction are held while connecting the detected
values sequentially, to prevent getting off the scale and to avoid
the resultant discontinuity of detected values.
As the wafer chuck moves further in the negative Y direction, the
wafer head units 21b and 21c overlie the wafer scales 22c and 22d,
while on the other hand the wafer head units 21a and 21b go out of
overlying the wafer scales 22a and 22d. Thus, when the detected
value of the wafer head unit 21c and the detected value of the
wafer head unit 21c (having operated hitherto) take simultaneous
values, these detected values are connected, such that a wide
detection stroke of the stage is assured.
The amount of movement of the wafer chuck in the X and/or Y
direction is detected on the basis of the principle of diffraction
grating interference, as described hereinbefore. Therefore,
instability of a detected value due to any environmental change as
in the case where a laser distance measuring device is used for the
detection, is avoided. Thus, the position of the wafer chuck 5 is
detected with good precision. Also, since a used diffraction
grating is a one-dimensional diffraction grating, the manufacture
of the same and the handling of the same are quite easy.
While the foregoing description has been made with reference to a
step-and-scan type exposure apparatus, the invention is applicable
also to a step-and-repeat type exposure apparatus: in such case the
plate member 18, the original head 23 and the original scale 24 are
not provided, and the original 3 is held fixed such that the
circuit pattern of the original 3 is printed at once.
[Second Embodiment]
FIG. 12 is a schematic perspective view of a second embodiment,
wherein a displacement detecting system of the present invention is
incorporated into an exposure apparatus. FIG. 13 is a schematic
view for explaining the positional relation among wafer scales of
the exposure apparatus of FIG. 12 as well as the positional
relation among wafer head units of the exposure apparatus.
In this embodiment, a plate member is fixedly attached to the lower
end portion of a barrel 52, and four wafer scales 72a, 72b, 72c and
72d are fixedly mounted on this plate member. Also, fixedly mounted
on the top surface of a wafer chuck 55, around a wafer 54, are four
wafer head units 71a, 71b, 71c and 71d. The structure and
disposition of these wafer scales 72a, 72b, 72c and 72d and of
these wafer head units 71a, 71b, 71c and 71d are similar to those
of the first embodiment. Further, the structure of the remaining
portion of the exposure apparatus is similar to that of the first
embodiment. Therefore, a description of them will be omitted
here.
In this embodiment as described above, the wafer head units 71a,
71b, 71c and 71d are provided on the wafer chuck 55. On the other
hand, the wafer scales 72a, 72b, 72c and 72d which are light as
compared with the wafer head units 71a, 71b, 71c and 71d, are
provided on the barrel 52. This allows simplification of the
holding mechanism to the barrel 52, and it enables stable
detection.
Next, an embodiment of device manufacturing method which uses any
one of the exposure apparatuses described hereinbefore, will be
explained.
FIG. 14 is a flow chart of the sequence of manufacturing a
semiconductor device such as a semiconductor chip (e.g. IC or LSI),
a liquid crystal panel or a CCD, for example. Step 171 is a design
process for designing the circuit of a semiconductor device. Step
172 is a process for manufacturing a mask on the basis of the
circuit pattern design. Step 173 is a process for manufacturing a
wafer by using a material such as silicon.
Step 174 is a wafer process which is called a pre-process wherein,
by using the so prepared mask and wafer, circuits are practically
formed on the wafer through lithography. Step 175 subsequent to
this is an assembling step which is called a post-process wherein
the wafer processed by step 174 is formed into semiconductor chips.
This step includes assembling (dicing and bonding) and packaging
(chip sealing). Step 176 is an inspection step wherein an
operability check, a durability check and so on of the
semiconductor devices produced by step 175 are carried out. With
these processes, semiconductor devices are finished and they are
shipped (step 177).
FIG. 15 is a flow chart showing details of the wafer process. Step
181 is an oxidation process for oxidizing the surface of a wafer.
Step 182 is a CVD process for forming an insulating film on the
wafer surface. Step 183 is an electrode forming process for forming
electrodes on the wafer by vapor deposition. Step 184 is an ion
implanting process for implanting ions to the wafer. Step 185 is a
resist process for applying a resist (photosensitive material) to
the wafer. Step 186 is an exposure process for printing, by
exposure, the circuit pattern of the mask on the wafer through the
exposure apparatus described above. Step 187 is a developing
process for developing the exposed wafer. Step 188 is an etching
process for removing portions other than the developed resist
image. Step 189 is a resist separation process for separating the
resist material remaining on the wafer after being subjected to the
etching process. By repeating these processes, circuit patterns are
superposedly formed on the wafer.
The foregoing description has been made to embodiments wherein a
displacement detecting system is incorporated into an exposure
apparatus. However, the invention is not limited to this, but it is
applicable also to a movable stage in a mechanical working machine
such as a high precision milling machine, a lathing machine or an
electron beam working machine, for example.
While the invention has been described with reference to the
structures disclosed herein, it is not confined to the details set
forth and this application is intended to cover such modifications
or changes as may come within the purposes of the improvements or
the scope of the following claims.
* * * * *